The invention is related to a fuel injection system of the type generally described herein and finally claimed. Fuel injection systems of this kind, intended in particular for Diesel motor vehicle engines, have an injection timing adjustment device functioning in accordance with rpm, which automatically compensates for the delay in injection onset at the injection nozzle which occurs at high rpm because of the long conduction paths. By the use of this injection timing adjustment device, which may also be called an automatic injection adjuster, the most favorable combustion and thus the maximum output of the Diesel engine are intended to be maintained even with widely variant rpm levels. However, it has been discovered that this is entirely true only when the air pressure conditions remain identical. For instance, if the Diesel engines are driven at high altitudes, then the capacity for ignition is restricted by the reduced air charge (lower final compression temperatures), and the ignition delay becomes larger, particularly at zero load and partial load. This causes both steep pressure gradients, and thus hard running on the part of the engine, and misfiring, which causes the emission of blue smoke.
A fuel injection system is already known having the general structure described with a fuel injection pump embodied as an injection pump of the distributor type (that is, with a distributor injection pump VE..F.. by Robert Bosch GmbH, Stuttgart, Germany; see, for example, the technical customer service manual VDT-I-460/1, second addendum of May, 1977 or the SAE Paper No. 760127 from the Automotive Engineering Congress in Detroit, Mich., held Feb. 23-27, 1976). In this pump, the position of a full-load stop of the rpm governor incorporated in the pump housing which determines the maximum permissible supply quantity is corrected in accordance with the charge pressure or the atmospheric pressure of the combustion air supplied to the engine. The hydraulic injection adjuster which functions in accordance with rpm and/or load does not, however, take into consideration the changed air pressure conditions that pertain to the combustion air, so that the disadvantages initially mentioned are not eliminated, despite the correction in supply quantity.
In a distributor injection pump known from the German Offenlegungsschrift No. 26 48 043, which has a hydraulic injection adjuster, a timing adjustment toward "early" is controlled in accordance with temperature and is superimposed on the injection adjustment controlled in accordance with rpm by means of a further change, controlled in accordance with temperature, in the presupply pump pressure exerted upon the adjustment piston of the injection adjuster. However, this timing adjustment toward "early" is effective only from the onset of starting until the warm-up of the engine. This apparatus is ineffective in the case of a warm engine, and the disadvantages mentioned above are not eliminated by this control apparatus either.